In drilling a well, the drill string is connected with the drill bit as the hole is deepened. Occasionally, the hole will deviate and form what is known as a key seat which tends to stick the pipe. At other times, there will be a failure of the drill string where the pipe is broken with part of the drill string retrieved, part of the drill string in the hole. In other instances, differential pressure sticking will grab and hold the drill string, often relieved by removing part of the drill string and leaving the lower end of the drill string in the hole. In a variety of circumstances exemplified by those listed above, it is sometimes necessary to remove the drill string, leaving a part of the drill string in the hole and thereafter conduct a washover operation. In doing this, a larger diameter pipe is lowered into the borehole and is stabbed over the remaining portion of the drill string which was left in the borehole. This portion is commonly known as a fish, and one procedure for removing the fish is a washover process. In washover, the drill string is removed and repositioned in the borehole with a large diameter pipe at the lower end. The wash pipe diameter is sufficient to telescope over the stuck fish. A large flow of drilling fluid is then introduced through the drill string and the wash pipe while rotating with weight on the drill string. The wash pipe is advanced to telescope over the fish. This washover will typically release the stuck fish and thereby free it so that the fish can then be retrieved from the borehole.
A successful washover job requires a large flow of fluid. The drilling fluid flow is almost unimpeded when the washover pipe is clear of obstructions. By contrast, the drilling fluid flow is impeded when going in the hole, if the wash pipe OD has little clearance in the well borehole, or if the OD of the fish has little clearance from the ID of the wash pipe when it is engaged. Both of these conditions tend to divert the flow of fluid up the drill string. This action will cause the drill pipe to overflow at the surface, and also will retard lowering the string into the well borehole because of the piston action created by the restricted fluid flow.
Successful washover operations do require a substantial flow delivered to the right portion of the borehole to complete a washover job. Consider as an example a 500' fish which is stuck in a key seat. Assume that the key seat is approximately half the length of the fish. The washover pipe is run into the well to extend over the stuck fish. Assume in this example that the drill bit forms a hole which is approximately 7 inches in diameter while the drill pipe of the fish is typically 4 1/2 or 5 inches OD. This leaves little clearance for the wash pipe to pass over the stuck fish. When the wash pipe telescopes over the drill pipe in the borehole, the stuck fish tends to plug the wash pipe thus forcing the fluid up the drill sting causing the drill string to over flow at the surface, impeding the process of lowering the string in the hole.
This apparatus is installed in a drill string at the top end of the wash pipe. It vents drilling fluid while the wash pipe is being stabbed into the borehole while it telescopes over the stuck fish. When the wash pipe is partially obstructed by the stuck fish partly in the bottom end of the wash pipe, the wash pipe is pushed onto the fish until such obstruction forces drilling mud in the well up the drill string. perhaps to spill on the rig floor. The present apparatus responds to this increase in pressure and bypasses drilling mud through ports isolated by a movable sleeve. The bypass route opens into the annular space above the wash pipe. The wash pipe may pass over the stuck fish without overflowing at the top end of the drill string. When the pump is turned on the sleeve is moved to close the ports and the flow from the pump is then directed to the bottom end of the wash pipe. This delivers the washover fluid at the location where it is most needed. This enables a more rapid retrieval of the fish in that the washover procedure is expedited; also, the rig floor is kept clean.
The method and apparatus of the present disclosure are thus summarized as providing a wash pipe for attachment to the lower end of a drill string to be run into a borehole to undertake a washover operation. The washover pipe is connected with the drill string thereabove by means of a tubular member which provides diametric transition as necessary between the larger wash pipe and the smaller drill string thereabove. On the interior, there is a lengthwise sleeve. In the up position, it aligns ports through the sleeve with ports in the outer wall. This serves as a bypass for drilling fluid forced upward through the drill string, thereby reducing the washover fluid flowing through the drill string to the surface. The sleeve is forced upwardly by means of a coil spring or collet spring. A restricted orifice at the top end of the sleeve makes it responsive to an increase in pump pressure. Where there is an increase in supply pressure and hence pressure drop across the restriction, the restriction and connected sleeve is then forced downwardly. There is also an unbalanced piston (pressure down) to help force the sleeve over the ports should the flow be restricted sufficiently to cause the restriction not to activate. When it moves downwardly, it closes off the ports in the sleeve, achieving an isolation by suitable seals and thereby preventing use of the bypass route for the washover fluid. The device preferably includes a latch mechanism which secures it in the down or closed position of the sleeve. An alternate embodiment is also disclosed.
A procedure contemplating washover assistance of fish retrieval is set forth. All of this will be detailed in greater detail on review of the present disclosure.